This invention relates to a measuring instrument, employing a hall element, for determining the value of a wide variety of parameters in a system. It is particularly useful in measuring electrical current of any waveshape, including d-c, a-c or d-c with superimposed a-c.
Current sensors have been developed wherein a hall element (or hall effect generator) responds to the magnetic flux, produced by the current to be measured, to provide a voltage which is proportional to and represents the current. A major advantage of a hall effect sensor is that it may be clamped on the conductor carrying the measured current and will be electrically isolated from that conductor. In one particular type of sensor, the hall element is subjected to two opposing magnetic fluxes, one produced by the current in the conductor to be measured and the other by a cancellation circuit. The current in the cancellation circuit is adjusted so that the two fluxes cancel each other, the net flux in the hall element thereby becoming zero. The amplitude of the cancelling current is therefore a function of, and provides a measure of, the magnitude of the sensed current.
Unfortunately, the accuracy of these prior hall element sensors suffers with temperature changes and aging. As a hall element ages or its temperature varies, its performance characteristics change and may even become non-linear. Hence, erroneous measurements may be obtained under those conditions. In contrast, the sensing system of the present invention, although also employing a hall element, achieves highly accurate measurements and is immune to the deleterious effects of temperature, aging and non-linearity. Moreover, these improved results are accomplished by means of a relatively simple and inexpensive circuit arrangement utilizing a low-cost hall element.